TEMPORARY FIX: set up the large libcurl connection pool for USDF

The size of the pool is configured specifically for the Qserv setup
at USDF, where there are 14 workers and 300 query result processing
threads. The pool allows up to 16 extra connections for other
activities which are not related to pulling result files from workers.
An idea is to allow as many connection as it's needed for the worst
case scenarios in order to prevent "socket leak" at Czar.

src/ccontrol/MergingHandler.cc

@@ -270,7 +270,7 @@ bool readHttpFileAndMerge(string const& httpUrl,
         http::ClientConfig clientConfig;
         clientConfig.httpVersion = CURL_HTTP_VERSION_1_1;  // same as in qhttp
         clientConfig.bufferSize = CURL_MAX_READ_SIZE;      // 10 MB in the current version of libcurl
-        clientConfig.maxConnects = 1024;                   // the cach size of the libcurl connection pool
+        clientConfig.maxConnects = 300 * 14 + 16;          // the cach size of the libcurl connection pool
         clientConfig.tcpKeepAlive = true;
         clientConfig.tcpKeepIdle = 5;   // the default is 60 sec
         clientConfig.tcpKeepIntvl = 5;  // the default is 60 sec